1. Field of the Invention
The invention generally relates to lasers and, in particular, to a system and method for suppressing multimoding behavior of lasers by reducing amplification of the side modes of light in the laser cavity. The reduction in amplification of the side modes is achieved by introducing asymmetric dispersion into the laser cavity to dispose the side modes asymmetrically about the fundamental mode.
2. Related Art
There are many different types of lasers which are well known in the art. A laser generally includes a light generation/amplification mechanism residing in a resonant cavity. The light generation/amplification mechanism includes a gain medium that produces and amplifies light. In general, the longer the light travels through the gain medium, the more the light is amplified.
To increase amplification of the light generated by the gain medium, two mirrors are typically located at opposite ends of the cavity, and the light generated by the light generation/amplification mechanism is reflected back and forth between the two mirrors numerous times. The gain medium amplifies the light each time the light is passed through it. Consequently, as the light is reflected back and forth between the two mirrors, the light is increasingly amplified.
Usually, at least one of the mirrors allows some of the light to pass through the mirror. Therefore, some of the light is reflected by the mirror and some of the light passes through the mirror. The light that passes through the mirror is used to form a laser beam that is output by the laser. This laser beam can be used to perform a variety of functions, such as optical signaling, for example, which is well known in the art.
It is the nature of most laser cavities that light at a plurality of discrete ranges of wavelengths (referred to as xe2x80x9cmodesxe2x80x9d) are appreciably amplified in the cavity. However, in many situations, it is desirable that the light forming the laser beam have a single predetermined mode or range of wavelengths. For example, a single wavelength range, referred to as the xe2x80x9cfundamental mode,xe2x80x9d usually receives the highest amplification. The other modes, called the xe2x80x9cside modes,xe2x80x9d are preferably suppressed so that only light having the highest amplification propagates from the laser. Failure to suppress the side modes is often referred to as xe2x80x9cmultimoding.xe2x80x9d
To suppress the side modes, many lasers position an optical filter in the cavity. The light being reflected between the two mirrors passes through the filter, and the filter attenuates any light outside of the fundamental mode and passes light in the fundamental mode. Alternatively, one of the mirrors can be configured to reflect. only light in the fundamental mode to filter the side modes. By filtering out the side modes, the laser can be configured to output only the fundamental mode of the light.
However, most conventional filtering means fail to effectively filter all of the light associated with the side modes. As a result, conventional lasers typically fail to adequately suppress multimoding.
Thus, a previously unaddressed need exists in the industry for providing an improved system and method of suppressing the side modes in a laser.
The invention overcomes the inadequacies and deficiencies of the prior art discussed above. In general, the invention provides a system and method for,suppressing multimoding by reducing amplification of the side modes in a laser cavity.
The invention uses a light generation/amplification mechanism and an asymmetric dispersion enhancer in a cavity of a laser. The light generation/amplification mechanism includes a gain medium that generates and amplifies light. The asymmetric dispersion enhancer receives the light generated by the gain medium and increases the asymmetric dispersion of the light. As a result, the side modes of the light passing through the cavity are asymmetrically disposed about the fundamental mode, thereby reducing the amplification of the side modes.
The invention also provides a method for suppressing multimoding. Briefly described, the method can be broadly conceptualized as including the following steps: providing a laser cavity; amplifying light in the laser cavity; filtering the light; and causing side modes of the light to asymmetrically distribute about a fundamental mode of the light.
The invention has many advantages, a few of which are delineated below, as mere examples.
An advantage of the invention is that light amplified by a laser and having a wavelength outside of a preselected range can be suppressed.
Another advantage of the invention is that amplification of side modes associated with light passing through a laser cavity can be reduced.
Other features and advantages of the invention will become apparent to one skilled in the art upon examination of the following detailed description, when read in conjunction with the accompanying drawings. It is intended that all such features and advantages be included herein in the invention, as is defined by the claims.